The present invention generally relates to electronically controlled motor systems and methods for upgrading an existing system to achieve a higher efficiency and comfortable operation for heating, ventilation and air-conditioning (HVAC) applications.
A new generation of motor control technologies have been developed in the past decade and sensorless control of permanent magnet synchronous motor (PMSM) systems have been applied in residential and commercial HVAC blower driven applications. These advanced PMSM systems are often referred to as advanced electronically commutated motors (ECMs) in HVAC applications. Advanced ECMs not only deliver high peak efficiency at rated working speeds, but also have a large high-efficiency operational speed range. For example, an advanced ECM can operate at a rated speed of 1,050 rpm with 89% efficiency, and at a low speed of 300 rpm, its efficiency can be at 70-80%, which can be critical for air circulation in a residential HVAC system.
Conventional HVAC blower motors are fixed speed or multiple speed permanent split capacitor (PSC) AC motors. A typical prior art domestic HVAC system 20 is shown in FIG. 1, and includes a legacy PSC motor 23. The PSC motor 23 has two or more winding taps that offer different operating speeds by reducing the magnetic field amplitudes when powered on with the voltage connections. In a heating or cooling mode of operation, one of the winding taps respective to the operating mode is turned on by a furnace main control board 24 that executes the signals or commands from a thermostat 22. Typically, the operating speed for the cooling mode is different from that for heating mode.
There are two AC voltage level groups of the components of the system 20, 120V and 24V. A power transformer 21 supplies the 24V voltage. The low voltage 24V from the transformer 21 is connected to power on the thermostat 22. Thermostat 22 provides multiple channels of AC voltage 24V signals representing the operational status, such as a high heat mode, or low cooling mode, etc. The signals are sent out through the terminals of a communication port and a cable, such as a multiple-wire cable 25, and can be sensed and detected by the furnace main control board 24. Different types of thermostats sold in market may have two, three, or five operational states or modes, with a three-mode thermostat typically including a heat mode, a fan only mode, and a cooling mode, and a five-mode thermostat typically including a high heat mode, a low heat mode, a fan only mode, a high cooling mode, and a low cooling mode.
The furnace main control board 24 is connected with the 120V voltage as well as the thermostat outputs through the multiple-wire-cable 25. Output wires 26 of the furnace control board 24 have two or four wires depending on the motor speed options, e.g., for a two-speed or four-speed system. The output wires 26 are each connected to a corresponding winding tap of the PSC motor 23.
A drawback of the PSC motor 23 is very low efficiency, such as about 20%, when running at low speed. Since the continuous fan operation for circulation mode is a preference in many households, low speed operation is very common, and so the prior art domestic HVAC system 20 tends to be inefficient overall.
Conventional blower motors, such as PSC motors, are being replaced with variable speed ECM blower systems. Retrofitting a system with a PSC motor to an ECM-based variable speed system creates significant customer benefits, including energy savings and increased comfort. Additionally, HVAC systems with legacy variable speed ECM blower systems have been applied to residential homes in the past decade. Because these legacy ECMs have been in operation for a long time, their expected life is at or close to the end. Such ECMs will need be replaced by a new ECM. These ECMs are variable speed motors, which are programmed to produce a set motor speed based on a thermostat call. Another popular ECM is the X13 motor available from Regal Beloit. The X13 motor is a constant torque motor and is programmed to produce a set motor torque based on the thermostat call.
Some configurations and connection methods have been developed for the replacement of legacy motors in existing HVAC systems. However, these either have complicated connection methods that are not practical for field installers, or have restrictions that limit motor performance, flexibility and customized setup in existing HVAC systems. Another issue particular to retrofitting legacy ECMs is that current ECMs used for retrofitting applications have to be specifically developed with unique software and hardware. These special ECMs add complexity into production and inventory management, which increases costs to the final customer.